Liquid conductivity measuring apparatus

Abstract

A salinometer apparatus for measuring the salinity (conductivity) of a liquid sample from a standard sample bottle or other container having an elongated tube having one end adapted for insertion into a sample bottle or container, a conductivity measuring cell formed of a glass tube having an elongated main body portion, four upwardly extending branch tubes connected to the main tube and having liquid seals at their upper ends, metal electrodes mounted inside the four branch tubes, two of the electrodes forming potential electrodes and the other two forming current electrodes, electrical leads passing through the seals and connected to the four electrodes, said cell being connected at one end to the elongated tube and the other to waste, a temperature controlled liquid bath, temperature changing means associated with said bath, an electric heating and control circuit connected to said heating means, the said conductivity cell and a portion of the elongated tube being immersed in said bath, means for flushing the conductivity cell between sample measurements, air pressure means for connection to the sample holder for positively forcing a portion of the liquid sample out of the sample holder into and through the elongated tube and conductivity cell, and a conductivity, measuring circuit connected to the potential and current electrode leads for measuring the conductivity of the liquid contained in the cell.

I claim: 
     
       1. A liquid conductivity measuring apparatus for measuring the salinity of a liquid sample from a standard sample bottle or other container comprising: a. an elongated tube having one end adapted for insertion into a sample bottle or container,   b. a measuring cell for measuring the conductivity of a water sample formed of a tube having an elongated main body portion connected at one end to the elongated tube and at the other to waste, four upwardly extending branch tubes connected to the main tube and having liquid seals at their upper ends, electrodes mounted inside the four branch tubes, two of the electrodes forming potential electrodes and the other two forming current electrodes, electrical leads passing through the seals and connected to the four electrodes,   c. means for controlling the temperature of said cell,   d. means for flushing the contents of the cell to waste between sample measurements, and   e. air pressure means for connection to the sample holder for positively forcing a portion of the liquid sample out of the sample holder into and through the said tube and into the means for measuring the conductivity, and   f. a conductivity measuring circuit connected to the potential and current electrode leads for measuring the conductivity of the liquid sample in the cell said circuit comprising: a standard resistance, a current source connected in series with the standard resistance and the current electrodes of the cell, a voltage comparator connected to the potential electrodes of the cell and to a source of regulated square wave voltage such as to compare the voltage across the potential electrodes and the square wave voltage such as to cause it to provide a current through the standard resistance and the current electrodes such that the voltage comparator is brought to a null, a linear voltage comparator connected across the standard resistance and to a voltage related to the regulated square wave voltage to compare this voltage and the voltage across the standard resistance and provide an output square wave voltage related to the conductivity of the cell, a square wave to DC amplifier connected to the linear voltage comparator for changing the output voltage to DC, a DC amplifier connected to the square wave to DC amplifier, and readout means connected to the DC amplifier.   
     
     
       2. A liquid conductivity measuring apparatus for measuring the salinity of a liquid sample from a standard sample bottle or other container comprising: a. an elongated, thin-walled heat exchange tube having one end adapted for insertion into a sample bottle or container, said tube having a relatively small diameter and being made of a material having high heat conductivity characteristics,   b. a conductivity measuring cell connected to the other end of the elongated tube and to waste,   c. a liquid bath with the conductivity measuring cell and a portion of the elongated tube immersed in the said bath such that, on passage of a liquid through the tube into the cell, its temperature rapidly approximates that of the liquid bath,   d. means for measuring the temperature of said liquid bath,   e. air pressure means for connection to the sample holder for positively forcing a portion of the liquid sample out of the sample holder into and through the said tube and into the conductivity measuring cell, and   f. means for flushing the contents of the said conductivity measuring cell to waste between sample measurements.   
     
     
       3. A liquid conductivity measuring apparatus as in claim 2 wherein the conductivity measuring cell is formed of a tube having an elongated main body portion connected at one end to the elongated tube and the other to waste, four upwardly extending branch tubes connected to the main tube and having liquid seals at their upper ends, electrodes mounted inside the four branch tubes, two of the electrodes forming potential electrodes and the other two forming current electrodes, electrical leads passing through the seals and connected to the four electrodes, and a conductivity measuring circuit connected to the said leads. 
     
     
       4. A liquid conductivity measuring apparatus as in claim 3 wherein the means for flushing the conductivity cell is a source of air connected to one of the said branch tubes such that on introduction of air, the cell is cleared of liquid. 
     
     
       5. A liquid conductivity measuring apparatus as in claim 2 wherein the means for measuring the temperature of said liquid bath is a temperature control means including a heating lamp connected to an electrical supply, thermoelectric cooling device connected to an electrical supply, and at least one thermistor immersed in the bath in spaced relation to the lamp and connected in the electrical supply to the heating lamp for turning on and off said lamp to effect thermostatic control of the bath. 
     
     
       6. A liquid conductivity measuring apparatus as in claim 3, wherein the conductivity cell is positioned in the apparatus such that the end connected to waste is lower than the end connected to the elongated tube and the means for flushing the conductivity cell is a controllable source of gas pressure connected to each of the four upwardly extending branch tubes.